1. Field of the Invention
The present invention generally relates to a washing machine, and more particularly to a washing machine that has a function for removing microorganisms propagating on an inner wall face of a washing tank with which the laundry comes into contact.
2. Description of the Background Art
When a washing machine carries out washing processes, soap dregs are deposited on an inner wall face of its washing tank. Microorganisms such as bacteria and fungi propagate with the soap dregs serving as a source of nutrition. The portions on which bacteria and fungi propagate basically include all the portions inside the washing tank. Microorganisms propagate not only on a bottom portion of the washing tank with which water is frequently made in contact usually, but also on, for example, portions along a water line on which stains are easily deposited as well as on an upper portion of the washing tank which is located above a water face in the maximum water level and with which water is not frequently made in contact, because water droplets form spray during the washing process and adhere thereto, and because water that has been raised along the inner wall during a dehydrating process remains thereon.
With respect to the portions such as the bottom portion of the washing tank with which water and the laundry are made in contact during the washing process, in the case when the washing process is carried out usually, the propagation of microorganisms is limited since these portions are washed every time the washing process is carried out. However, with respect to the upper portion of the washing tank, since such a washing effect is weak, microorganisms tend to vigorously propagate. When the washing process is repeated under these circumstances, microorganisms are dispersed in the washing water to cause a problem that the laundry is stained. Moreover, when microorganisms propagate in the washing tank, a problem of scattered microorganisms into the living environment might occur, and a visually unpleasant feeling tends to be given to the user. In order to solve these problems, a washing machine provided with a tank washing function has been proposed.
For example, Japanese Patent Application Laid-Open No. 2004-321683 has proposed a washing machine in which: in order to effectively disperse a chemical solution having an antibacterial property onto portions that tend to allow microorganisms to propagate, a rotatable washing tank, a water receiving tank that encloses the washing tank and a chemical solution in which an antibacterial agent has been dissolved are provided, and the chemical solution is scattered by the centrifugal force derived from the rotation of the washing tank to be dispersed onto the outside of the washing tank or the inside of the water receiving tank.
Moreover, Japanese Patent Application Laid-Open No. 9-56972 has proposed a washing machine in which: in order to sufficiently provide a washing effect to the tank, a tank washing course is prepared, and during a water supply process or during a water draining process, the water supply process or the water draining process is suspended at a plurality of stages of water levels that are lower than the final arrival water level to stir the water held in the tank or the water remaining in the tank for a predetermined period of time.
Moreover, Japanese Patent Application Laid-Open No. 2000-308793 has proposed a washing machine in which: in order to cleanly wash the washing tank compatibly used as a spin drier tank in a tank washing course, the washing tank compatibly used as a spin drier tank, which is placed inside an outer tank so as to freely rotate, is provided, and an overflow outlet, which is placed at a position above the water level set in the washing course and used for discharging water that has come to this level, is provided in the outer tank, and during a driving operation of the tank washing course, a pulsator is rotated so that water held inside the outer tank is stirred and thus overflows from the overflow outlet.
The tank washing process, proposed in Japanese Patent Application Laid-Open No. 2004-321683, is provided with a washing machine of a double tank structure provided with an inner washing tank (inner tank) and an outer washing tank (outer tank), and aims at the outer tank so that a chemical solution is dispersed outside the inner tank or inside the outer tank to carry out the washing process. In other words, the chemical solution is dispersed between the inner tank and the outer tank, with the result that no chemical solution is made in contact with the wall face on the inside of the washing tank with which the laundry is directly made in contact. Here, a water holding chamber is prepared separately from the inner tank and the outer tank, and it is necessary to use water in the water holding chamber so as to disperse the chemical solution.
Even in the case when a chemical solution is added to the water inside the inner tank and the outer tank so that the water and the chemical solution are allowed to move and flow along the wall face by the centrifugal force, since through holes are formed in the wall face on the inside of the inner tank, the water and the chemical solution flow out through the through holes, failing to be entirely dispersed over the wall face. Although there is the possibility that, for example, the wall face inside the inner tank, that is, portions near the water line and upper portions thereof, might be subject to propagation of bacteria and fungi, the tank washing processes, proposed in the above-mentioned patent publications, do not allow the chemical solution to make contact with the corresponding portions, thereby failing to properly provide the sterilizing and antibacterial effects.
In a washing machine proposed by Japanese Patent Application Laid-Open No. 9-56972, the water supplying and draining operations are suspended in multiple stages to carry out stirring processes. This system aims to wash portions near the water level by carrying out the stirring processes while the water level is changed step by step. For this reason, in order to wash the upper portion of the washing tank above the maximum water level, the stirring process needs to be carried out at the water level near the maximum water level, causing a large amount of water consumption.
Moreover, since a plurality of washing processes are carried out step by step, the driving time of the washing machine is prolonged, with the result that the corresponding increased power consumption is required. In recent years in which the number of two-income families is increasing, the smaller the time required for laundry washing, the better from the viewpoint of convenience. Under the current trend that the shortened driving time of the washing machine has been demanded from the viewpoints of energy conservation and convenience, prolonging the driving time of the washing machine so as to wash the tank is to swim against the current.
The washing machine, proposed in Japanese Patent Application Laid-Open No. 2000-308793, needs to hold water in the outer tank virtually up to the maximum water level so as to wash the tank, making it necessary to use a large amount of water resource. Consequently, in the current trend of making products that impose little load onto the environment, this washing machine fails to take the environment issue into consideration.